1. Field of the Invention
This invention relates to a mobile scaffold that longitudinally traverses a first track and a vertically spaced second track. More specifically, the invention pertains to such a scaffold with means for positioning an operator's platform both in elevation and in a lateral direction relative to the tracks.
2. Description of the Prior Art
In a manufacturing plant for large machines, such as cranes, there existed a problem of positioning painters for painting the machines within a paint booth. Ladders were considered to be unsafe at the heights required, particularly when used on an open grating of a down-draft paint booth or on the rough deck of a railroad flat car. Scaffolds and platforms could be used for a limited number of machine sizes, but where a wide variety of different size machines arrive at the work area in random order, such structure is unacceptable from the standpoint of safety, flexibility, and maintainability because this approach requires covering along the entire length of the product line.
Various cranes and other lifting devices have been used for positioning painters or other workmen at a work area. U.S. Pat. No. 3,357,517, that issued to Wagner on Dec. 12, 1967, shows a painter's mobile scaffold with two parallelogram lifts that are interconnected by an intermediate support member for horizontal rotation of the lowermost lift relative to the uppermost lift. The uppermost lift is attached to a vehicle that travels along a bridge deck, while the lowermost lift supports a platform for positioning a painter to paint the underside of the bridge deck. A platform positioning mechanism for use while working upon airplanes is shown in U.S. Pat. No. 3,602,335 that issued to Gustetic on Aug. 31, 1971. An upper base, that is mounted by beams and rollers for horizontal movement near a room ceiling, has a vertical mast depending therefrom. This mast includes a movable telescopic portion upon which is mounted a vertically slidable carriage. Supported upon the carriage is an operator's platform for rotation in a horizontal plane about the carriage.
U.S. Pat. No. 3,043,395, that issued to Volkel on July 10, 1962, shows a parallelogram lift that is mounted at one end upon a carriage and this lift supports at its outer end an operator's cage. A cylinder, controlled from the operator's cage, actuates the lift for up and down movement of the lift. Other patents that show lifts with parallelogram linkages include U.S. Pat. No. 3,176,792 that issued on Olson on Apr. 6, 1965, U.S. Pat. No. 3,534,832 that issued to Rediske on Oct. 20, 1970, and U.S. Pat. No. 3,807,575 that issued to Merrick on Apr. 30, 1974. A traveling overhead crane that supports an up-draft paint booth for painting airplanes is shown in U.S. Pat. No. 2,829,582 that issued to Abbott et al. on Apr. 8, 1958.
All of the patents mentioned above require a carriage for longitudinal travel along a floor or a ceiling. Near the floor of a down-draft paint booth, lateral clearance between a booth side wall and a large machine to be painted should be limited to reduce the volume of air required for circulation within the paint booth. Thus, a mobile scaffold must be able to fit within the limited lateral clearance. Furthermore, the carriage should not block the air flow through the open grating at the floor of the booth. Carriages that are mounted to travel along high ceilings require a substantial depth of an intermediate support structure to position a painter's platform near a work area, and such structure adds to the cost of the mobile scaffold. The ambient conditions within a paint booth make the booth an extreme fire hazard area. These factors had to be considered in developing the mobile scaffold that is disclosed in this application.